Internal combustion engines generally include an exhaust after-treatment device, such as diesel particulate filters, three-way catalysts, and the like. The exhaust after-treatment devices have been developed to effectively limit exhaust emissions from an internal combustion engine. In the case of compression-ignition or diesel engines, a great deal of effort continues to be expended to develop practical and efficient devices and methods for reducing emissions of largely carbonaceous particulates in exhaust gases. An oxidation catalyst is one of the devices that are often provided in diesel engines for such a purpose.
Typical exhaust systems incorporate an oxidation catalyst to reduce emissions from diesel engine. The oxidation catalyst oxidizes hydrocarbons (HC) and carbon monoxides (CO) that are formed in the combustion process of the engine. During its operative life, oxidation catalysts gradually reduce in efficiency. Diagnostic systems incorporated in a vehicle may be used to determine the efficiency index of the oxidation catalyst during an exhaust system regeneration process. However, the diagnostic system may be unable to differentiate whether an oxidation catalyst is operating below normal operating parameters during the regeneration process.